A “solar panel” is a set of solar photovoltaic modules electrically connected and mounted on a supporting structure. A photovoltaic module is a packaged, connected assembly of solar cells. The solar module can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications, and as such solar panels are widely used throughout the world.
A photovoltaic system typically includes a panel or an array of photovoltaic modules, an inverter, and sometimes a battery and or solar tracker and interconnection wiring.
Each photovoltaic module is rated by its DC output power under standard test conditions, and these typically range from 100 to 320 watts. One disadvantage of a solar panel is that as the temperature of the collecting surface increases, the efficiency of the solar panel significantly decreases. A conservative estimate by manufacturers (and used by some researchers) is that every 1° C. of temperature rise corresponds to a drop in efficiency by 0.5%. Based on our testing, with standard 100 W solar panels, a more realistic estimate is that for every 1° C. of temperature rise above 25° C. in cell temperature, there is a reduction between 0.5% and 1.5% of peak output. As the cell temperature increases further, there is a larger reduction in efficiency.
A photovoltaic panel is designed to operate with DC (direct current) electrical output. DC electrical current does not travel well over long distances. For example as much as 10% of the electrical power outputted from the panels can be lost through the wiring of a normal household photovoltaic installation. In photovoltaic solar farm situations many panels are connected together in series to form a larger group to deliver and produce a higher DC voltage in an effort to reduce the losses of long distances, however, 5-8% can still be lost throughout such a system.
MPPT (Maximum Power Point Tracking) devices are used to boost output performance of solar panels. Under most conditions the output performance can only be raised by 10% approximately, but the electronic MPPT device also consumes power in its operation. Other devices commonly referred to as DC/AC inverters, such as pure sign wave grid connect or grid ties have been implemented to convert the DC current delivered from the solar panels into high voltage AC output which travels to AC more readily over long distances. Losses through large electronic equipment still occur.
Domestic and some smaller commercial solar power systems use some form of storage system and DC/AC conversion system to connect directly to the domestic grid. All these applications result in losses of electrical energy. In the case of MPPT and grid connect devices this loss is through heat dissipation through the body of the devices and grid connect as well as internal losses. An additional offset and cost of these devices is in the heavy aluminium structure casing which is used as a heat sink to dissipate the heat. This cost must also be considered as a negative return on invest. It is known that you can harvest more power from an array of photovoltaic cells by eliminating connection in strings or reducing the length of strings by providing MPPT control to the individual or smaller number of cells. This is discussed at paragraph [0031] of US patent publication No. 2014/0306540 (Wu et al.). Such a solution is described in U.S. Pat. No. 8,093,757 (Wolfs et al.), where taking advantage of recent advances in low voltage electronics, maximum power tracking devices for very small groups of solar cells or for single cells are used to maximize power output from the array. The embodiment for Wolfs however, is primarily described with reference a solar powered vehicle, where movement of the solar powered vehicle causes some form of cooling due to air flow passing over the solar cells.
Whilst placing MPPT and inverter/grid connect devices closer to the DC output of the photovoltaic cells would improve efficiency, the downside is the temperature of such environment. In stationary solar panels of the type mounted on dwellings and buildings, photovoltaic cell temperature can be over three times that of ambient temperature. This means, that at an ambient temperature of 20° C., the cell temperature of a photovoltaic panel surface may already be over 60° C. This causes difficulties in placing MPPT and inverter/grid connect devices in close proximity to photovoltaic cells. Where solar panels are mounted in domestic and commercial situations, the MPPT and inverter devices are typically mounted downstream from the panels, and their typical operating temperatures are at about 50-70° C. at these downstream locations. To place the MPPT and inverter devices close to the high temperatures at which conventional solar panels operate, means that their internal temperature could get over 100° C., and this means their efficiency and service life is considerably compromised.
Furthermore, with conventional arrangements there is a compounding of losses. Firstly there are the losses in the photovoltaic cells panels themselves, discussed in detail in the background of our earlier patent application No. PCT/AU2015/050309 filed 5 Jun. 2015, and secondly you have the additional losses of the downstream positioning of MPPT devices and/or DC/AC inverter/grid connect devices.
One way of addressing this is to mount MPPT and “inverter/grid connect’ devices close to the DC output of the solar panel, and provide cooling thereto. However, any energy gain of placing the MPPT and inverter/grid connect devices closer to the DC output must be considered against the energy expended to cool such devices. As such there has not been any commercially viable cooling solutions, so the practice in the prior art has been to typically locate MPPT and inverter devices significantly downstream of the array of solar panels requiring lengthy DC cabling and its associated losses.
The present invention seeks to provide an apparatus for generating electricity that will ameliorate or overcome at least one of the deficiencies of the prior art.